Ethnic differences in hypertension and hypertension-related diseases may be due to differences in the mechanisms regulating blood pressure (BP) and BP reactivity. This project will examine the relationship between plasma insulin on the one hand and blood pressure (BP) and BP reactivity on the other as a function of obesity, fat distribution, lipoprotein profile, catecholamine concentrations, sodium flux, and ionized calcium concentration. The proposed study will examine 480 healthy men and women aged 25-44 years from three ethnic groups: 1) white nonHispanics; 2) black non-Hispanics; and 3) white Cuban Americans. We will assess BP and BP reactivity under three experimental conditions: 1) at rest; 2) in response to three standardized behavioral tasks in the laboratory; and 3) while ambulatory in naturalistic settings. Several psychosocial dimensions of behavior will be measured including anger and hostility. We will quantitate several hormones including insulin (fasting and after a glucose load), epinephrine and norepinephrine, cortisol, plasma renin activity, and aldosterone to better study their interrelationships with BP. We will also investigate the influence of sodium transport on blood pressure and how sodium transport is effected by hormones. In addition, the role of hormones on ethnic differences in the lipoprotein profile will be studied. Ethnic differences in obesity, fat distribution, physical activity and other covariates will be taken into account in the analyses. This study should provide valuable insight into mechanisms through which biobehavioral factors interact to affect blood pressure regulation.